Hydro-therapeutic treatment apparatus, such as spas, hot tubs and whirlpool baths, usually involves a tub having nozzles in its side-walls to which water is supplied by an electrically powered centrifugal pump. The water in the tub then is recirculated back to the inlet of the pump. Manifestly, it is desirable for an occupant of the tub to be able to regulate the velocity or flow of the water exiting, sometimes as jets, from the various nozzles mounted in the sides of the tub. In the past this has been accomplished by controlling the motor of the pump to provide a high or a low speed with commensurate flow, i.e. by a control which changes the motor windings. Desirable continuously variable or incremental regulation is not provided with such a control, however, because such a motor would be prohibitively expensive for hydro-therapeutic treatment apparatus, especially for a spa, hot tub or a whirlpool bath. It also has been suggested to continuously regulate the flow by a flow control valve mounted between the pump and the lines or piping supplying the water to the tub nozzles, such as disclosed in the U.S. Pat. Nos. to Friend, 2,772,421, Dec. 4, 1956, Kline, 4,110,852, Sep. 5, 1978, and Henkin et al, 4,679,258, Jul. 14, 1987. It has been found, however, that such a flow control valve mounted between the pump outlet and the water supply lines to the nozzles causes a considerable amount of noise when the pump is in operation. Since the valve is usually mounted adjacent the tub, such noise is disturbing to an occupant of the tub. Moreover, the valve operating knob or handle usually has been in a location not readily accessible to an occupant of the tub, necessitating getting out to operate the valve and regulate the flow.